In order to provide position information in GPS positioning signal undetectable places such as an indoor place or an underground shopping center, a known system includes an indoor transmitter. The indoor transmitter is installed in the indoor place to transmit a positioning signal indicating an indoor position to a portable terminal (e.g., JP 4296302B corresponding to US 2009/0115661A).
The inventor of the present application has found that the technology described in Patent Literature 1 involves the following disadvantage. In order for the portable terminal to receive the positioning signal from the indoor transmitter, all of the existing typical portable terminals should be replaced.